Sectoring is a well known technique for providing distinct coverage area from individual cell sites and can be achieved with “smart antenna” technology, which is well known in the art. Smart antenna methods dynamically change the radiation pattern of an antenna to form a “beam,” which focuses the antenna's topographical coverage.
Beam forming is an enhancement on sectoring in that the sectors can be adjusted in direction and width. Both techniques are employed to: 1) reduce interference between cells and the user equipment (UE) deployed within the cells; 2) increase the range between a receiver and a transmitter; and 3) locate a UE. These techniques are usually applied to the dedicated channels of the UEs once their general location is known.
Prior to knowing the location of a UE, the common channels broadcast information that all UEs may receive. While this information may be sent in static sectors, it is not sent in variable beams. There are inherent inefficiencies in this approach in that extra steps are required to determine the appropriate beam to use for the dedicated data exchanges. Additionally, the beams must be generally large enough to provide a broad coverage area, which in turn means their power with distance from the transmitter is lower. In such cases, they must use higher power, have longer symbol times and/or more robust encoding schemes to cover the same range.
Common channel coverage using a prior art scheme is shown in FIG. 1 as four overlapping wide beams. This provides omni-directional coverage, while giving a degree of reuse to the cell site. It also provides a coarse degree of directivity to the UEs (UE1, UE2) detecting one of the transmissions, by having each sector transmit a unique identifier.
Referring to FIG. 2, downlink dedicated beams between a primary station (P) and several UEs (UE3, UE4) are shown. Assuming the same power from the primary station (P) for FIGS. 1 and 2 and all other attributes being equal, the UEs (UE3 and UE4) shown in FIG. 2 can be further away from the primary station P than the UEs (UE1, UE2) shown in FIG. 1. Alternatively, the coverage areas can be made approximately the same by decreasing the symbol rate and/or increasing the error correction coding. Either of these approaches decreases the data delivery rate. This also applies to the receiver uplink beam patterns of the primary station P; and the same comments about coverage and options apply for data from the UEs to the primary station P.
In the prior art, the range of a primary station P or a UE is generally increased by combinations of higher power, lower symbol rates, error correction coding and diversity in time, frequency or space. However, these methods yield results that fall short of optimized operation. Additionally, there is a mismatch between the common and dedicated communications channels in the ways that coverage is aligned.
There exists a need for efficiently covering a sectorized cell without the drawbacks associated with prior art schemes.